The present invention relates generally to a method of making a railcar. More specifically, the invention relates to a method of manufacturing a multiple axle railcar having cambered span bolsters.
When a railway transports oversized or heavy cargo, it must account for the loading of each axle supporting the weight of the oversized load. To accommodate the excessive load, railways utilize railcars having additional axles compared to standard-capacity railcars. With the load distributed over a greater number of axles, the weight carried by each individual axle is reduced. However, railcar manufacturers must account for the turning performance of the multiple axle railcar, which can be diminished as the number of axles increases. Typically, multiple axle railcars have groups of truck assemblies connected by a span bolster, with a bolster located at each end of the railcar. The span bolster, in turn, attaches to the rail car at a pivot point near the center of the bolster. In this configuration, a multiple axle railcar is able to perform similarly to a standard railcar with a single pivoting truck at each end of the railcar.
An example of such a railcar is a twelve-axle rail vehicle manufactured by Kasgro Rail Corp. and disclosed in U.S. Pat. No. 5,802,981. The twelve-axle railcar has three sets of trucks, or six axles, at each end of the vehicle. The three trucks at each end of the railcar are mounted to a common carrier that distributes the load, otherwise known as a span bolster. The benefit of twelve-axle railcar, in addition to its load carrying capability, is improved turning performance resulting from the fact that one span bolster can pivot independent of the other.
The increased load carrying capability of the twelve-axle railcar, or any other railcar having additional axles, is the result of evenly distributing the weight of the cargo to maintain reasonable wheel and axle loadings. While twelve-axle railcars improve loading, situations can exist where there is a significant variance between each of the axles. For example, the center truck of a three truck set will often have a higher loading than each of the outboard trucks as it is located below the attachment point to the rail car body. Having equal loading on each axle provides numerous benefits, such as improved safety of operation and reduced maintenance costs. It would therefore be advantageous to develop a method of manufacturing a multiple axle railcar having a span bolster in a manner that minimizes manufacturing variances and promotes consistent loading across each axle.